1. Field of the Invention
The present invention relates generally to a code division multiple access (hereinafter referred to as “CDMA”) mobile communications system, and more particularly to an apparatus and method for transmitting and receiving data according to the radio link protocol (RLP) in a CDMA mobile communications system.
2. Description of the Related Art
The current IS-95 standard provides for wireless voice communication while the new CDMA 2000 standard provides or high-speed data communication including voice communication. The CDMA2000 standard enables the CDMA mobile communications system to provide services such as high-quality voice and moving picture communication as well as Internet access.
FIG. 1 describes the packet data services provided by the CDMA 2000 standard. A mobile station (MS) comprises terminal equipment (TE), and a mobile termination (MT). The base station (BS) is shown together with the mobile switching center (MSC) indicated by BS/MSC. Also shown is the interworking function part (IWF) for connecting the BS/MSC with a data network such as the Internet. The IWF serves to adapt different protocols employed by two communication parties. Web service parts of both MS and IWF exchange data with each other through Internet protocol (IP) processors and point-to-point link protocol (PPP) processors. Namely, the data produced by the web service parts are converted into link protocol packets and delivered to the lower layers for transmission according to a proper protocol. The web service parts may also be referred to as upper service parts.
As shown in FIG. 1, the link protocol packets transferred through the EIA-232 controller to the MT are delivered through the RLP part and are divided into an RLP frame. The RLP frame thus produced is transmitted through the physical channel connected according to the CDMA 2000 specification (IS-2000). The RLP packets are recovered by the BS into the link protocol packets transmitted through the relay layers to the IWF. Generally, the interface between BS and IWF meets the IS-658 specification. In the IWF, data is extracted from the link protocol packet and transferred through the IP processor to the web service part.
Though the above description shows the process of transmitting data from MS to BS, a similar process applies to the process of transmitting data from BS to MS. The system as shown in FIG. 1 may be modified to provide for a variety of communication services according to the CDMA 2000 standard, but it is common to transmit all the link protocol packets containing the web service data through the RLP part over the radio physical channel.
FIG. 2 is a block diagram illustrating the structure of an apparatus for transmitting and receiving data according to RLP in a mobile communications system. FIG. 2 shows, as a single frame, the structure for establishing a physical channel between MS and BS by the physical layer processor 150, 250 in order to transmit the RLP frames from the RLP processor 130 through the opposite physical layer to the opposite RLP processor 230.
The multiplexing/demultiplexing controller (hereinafter referred to as “MUX/DEMUX controller”) 140, 240 attaches the information of the destinations, sizes, etc. to the respective RLP frames transferred to the physical layer processor 150, 250, and analyzes the information attached to the received RLP frames transferred to the upper RLP processor 130, 230.
The transmission and reception data buffers 122, 124, 222, and 224 are memory devices for storing data transferred from the link protocol processors 110 and 210 to the EIA-232 or IS-658 controller, as shown in FIG. 1. The transmission data buffers 122 and 222 sequentially transfer the stored packets to the RLP processors according to the size demanded by them. On the contrary, the reception data buffers 124 and 224 sequentially store the data received from the RLP processors 130 and 230, delivered by the EIA-232 or IS-658 controller to the PPP processor or IWF processor. The EIA-232 and IS-658 controllers control the data exchanged between the data buffers 122, 124, 222, 224 and the link protocol processors 110, 210. FIG. 2 does not show the EIA-232 and IS-658 controllers because they may be replaced by other suitable means in the present CDMA 2000 packet services.
Meanwhile, according to RLP Type-3, the RLP processor 130, 230, as shown in FIG. 2, only produces the RLP frame of a size to fill the physical channel frame of 9.6 Kbps or 19.2 Kbps for rate set 1 (i.e., a transmission rate corresponding to a multiple of 9.6 Kbps), or 14.4 Kbps or 28.8 Kbps for rate set 2 (i.e., a transmission rate corresponding to a multiple of 14.4 Kbps). Hence, for the physical channel frame of a high transmission rate of 153.6 Kbps or 230.4 Kbps, a method is used to fill a single physical channel frame with a plurality of RLP frames, e.g., to transmit at maximum 9 RLP frames per 20 ms. Thus, if 9 RLP frames per 20 ms are transmitted in the RLP Type-3 specification, there occur RLP frames with the same respective sequence numbers as previous ones after 560 ms because the maximum number of the RLP frames distinguished by the 8-bit sequence number field is 256. This means that retransmission of a failing frame should be accomplished before the RLP frames with the same sequence numbers occur. Namely, different frames cannot be distinguished when they contain the same sequence numbers, therefore, it is impossible to request a failing frame with the same sequence number as the previous one. Thus, a failing frame should be retransmitted before another frame occurs with the same sequence number.
However, since the wired transmission protocol, such as TCP/IP, is designed to work in a reliable channel environment, the data packets produced by the wired transmission protocol may require several retransmissions for a complete transmission in a wireless transmission environment. Hence, if there is provided a method for assigning a unique sequence number to an RLP frame for one second or more, instead of 560 ms, retransmission of an RLP frame containing errors may be accomplished regardless of the number of times requesting the retransmission. Thus, considerable improvement of the performance and accuracy of the wired transmission protocol is achieved.